The invention relates generally to apparatus and processes for inspecting containers and other objects and deals more particularly with apparatus and processes for optically detecting flaws in and other features of such objects.
Flaws in glassware may take the form of checks, and three common types of checks are vertical splits, horizontal ring checks and horizontal thread checks. Often the checks occur in the finish portion of the glassware, and are objectionable because they seriously weaken the glassware and lead to fractures.
A previously known apparatus for detecting such checks comprises a plurality of incandescent lamps, each of which directing light to a different, localized portion of the container finish, and a plurality of optical sensors positioned to receive the light of associated ones of the incandescent lamps after reflection from a check. The incandescent lamps and sensors are supported at an inspection site at which site the containers are rotated to expose each check in the finish portion to illumination by at least one of the incandescent lamps and viewing by at least one of the sensors.
Because the shape and location of each check cannot be accurately predicted, the incandescent lamps and sensors are positioned experimentally to detect checks in test containers. During such experiments, first the incandescent lamp is positioned to project light toward a checked finish region at a previously determined angle relative to the horizontal. Then, the test container is rotated and an operator visually determine an angle at which a check in the container reflects light from the associated incandescent lamp. Finally, an optical sensor is positioned along this reflective angle. This procedure is repeated for each pair of incandescent lamp and associated optical sensor. It should be noted that the visible nature of the light from the incandescent lamp facilitates the set-up procedure.
While this system has proven effective, some difficulties have been experienced in providing an adequate signal to noise ratio for the light reflected from the checks because the light emitted by the incandescent lamps is qualitatively indistinguishable from ambient light. Also, there have been some difficulties with cross-talk because light from each incandescent lamp may occasionally reflect to the optical sensor of another incandescent lamp. If such reflections result from illumination of a non-defective region of a container, then a non-defective bottle may be deemed defective and later rejected.
U.S. Pat. No. 3,851,975 to Serret discloses inspection apparatus comprising an incandescent lamp, a mechanical modulating disk located between the incandescent lamp and a container, a plurality of optical sensors and a plurality of electronic receivers connected to the optical sensors. The modulating disk comprises a plurality of groups of orifices, the orifices of each group being evenly spaced and concentrically located about the disk axis. Light from the incandescent lamp passes through each group of orifices and is chopped to form a pulsing illumination pattern. The number and spacing of orifices of each group are different than the number and spacing of the orifices of the other groups so that the light passing through each group has a different pulsing frequency than the light of the other groups. Each receiver is tuned to the frequency of the emitted light of an associated optical sensor. Consequently, the light modulated by each group of orifices and reflected by the container can be distinguished from the light of the other orifices so that cross-talk is minimized. Such tuning also improves the signal to noise ratio. However, for some applications, the mechanical system of the 3,851,975 system may be too bulky and susceptible to vibrations which introduce other modulation frequencies.
Accordingly, a general object of the present invention is to provide inspection apparatus for detecting flaws in and other features of containers which apparatus provides a high signal to noise ratio, low degree of cross-talk, manageable size and lack of moving parts. A related process is also desired.